Aircraft landing wheel shimmy damper



Dec. 8, 1953 B. E. ocoNNoR 2,661,915

AIRCRAFT LANDING WHEEL SHIMMY yDAMPER Filed June 4. 1949 2 Sheetsheet 1 .F 15.1 .F 15E I LQ Qs Bernard E. 0 'C'ozzzzor /Q 254 5% @im ci@ uff/72255 Dec. 8, 1953 B. E. o'coNNoR 2,661,915

AIRCRAFT LANDING WHEEL SHIMMY DAMPER Filed June .4'.-` 1949 Z'Sheets-Sheet 2 WM @fm umg/L55 Patented Dec. S, 1953 "attrait ist M K AivniERr y 'licencia- EQ u(f )iirnnon Buffaloi N.y ssieriff Hougaillgggersheyorporation, Detroit, vMich., a corporation of Michigan Application miie-4, 1949,serie1'No. 97,231

This invention relatesto improved means ior preventing shimmy inrelatively swiveling struc,- tures,A and is more particularly' concernedwith preventing shimm-y' in Wheel supporting struc-,- turespsluch as swiveling aircraft landing wheel assemblies.

.-An important object of the present invention isv toV provide. 'ar nsliimmy damper construction whichgis vadapted for usein an assembly wherein relative s\wiveling movement isa functional requirement b 'ut which; due to varicusfactors, l is subject to vibrations or air pressure forcest'endingto'ei'ecta shimmyaction in 'one of the relatively swiveling structures; y l

Another .object of they invention .is to lprovide a shimmy damper construction which is especially useful in swiveling 'landing wheel assembliesl-voi aircraft and is'adapted to beincorporated therein without substantially altering the general struc,-

tur'al relationships of the operating components if of the Wheel a'sS'seIbly.' Al further' object of the ihventiorris to provide a shimihy'damper which is ,especially constructed for use' in they slip ring of the tcrque'scissorscon.- nctioii with the strut 0i aswivel type aircraft whe'el assembly;

Still another object of the inventionis. to pro-- vide 'a shimm-y damper; especiallyiuseiuiior use inaircraft landing wheel assemblies, which is oprable 'with' substantially'eqal ecieiicy under great extremes of temperature ccnditionsr-, t

A'fstillfurther object of tlie invention is to provide' ari improved shimmyzdamperlfor the general purposes described which kis simplein construction, cnomicalto produce `and assemble aiii duraoiea'nu ei'r'icient inservice.

Other objects; features and advantages lof the present iiiv'eiitioi'i win oe readiiy, apparent, from trievv iouovvingidetaiied description o'i e preferred embodiment taken in conjunction with` thev aci' "ying drawings; in which: Fi e' '1 'is`Y a fragmentary rear elevational view of evviv'e1 type aircraft' landing 4gear showiiig thjejcoiiueetioii tetvveen the reiativeiy swiveli'rie 'portions of trien gear;

5' a sectional vieweiiiiiiartoy Figure 2li (Olgiate-it) 3 but showing a slightly modied damper struc# tureiand f Figure 6 is a. fragmentary horizontalsectional view. taken on substantially the line `VL--VI of Fgllfe.' n @i The present invention is, well adapted;for;V use withan aircraft landing wheel assemblylsuchas shownin Figures 1 and 2 fordamping shimmy inthe wheeland the Wheel carriagesucha Wheelcarriage includes a strut YH) whichis generi ally of the oleo 'strut type and a swivel leghor wheel yoke Il which carriesV the Astud .shaftprovidin'gthe Wheel axle (not .shown Projecting from the yoke H vis a cylinder l2 which lextentie rotatably and reciprocably up into a cylindrical tubular casing ,|3 having bearing. structure I4 therein for the cylinder l2.

In ,order to dampen shimmy in the wheeljsupf porting .gear including; the .yokeA I l, a novel shimmy'damper assembly l5 is provided This damper has a Working lamplitude of 360 so as to permit full turning of the wheel about the axis of the cylinder i2'. It is operable Withsubstantially constant eiiciencyunder extremes of temperature variations. It 'isr highly ecientfor damping shimmy, that is, rapid rotary orfoscilla-r torymovements and especially, such movements tending to assume anundesirable vibrational fre:

quen'cy,.whi1e nevertheless permitting. freeiand Adiiiir of a hubiing L9E w "iii encircles eas '3 .below ari riulr limit Shoulder Vfle the'cesilg A 'id IiOIiIQtry llit merite hun. It andthe/eene screed means' of e key member r2| fitting in e keyvviiy' 22 iii the easing I3 and a lieyway '23 in th inner-pe: rip'hery ofthe' hub ring;y The axial positionner the hub ring l 9 against the shoulder 2li is -maintained by a nut 24 turned upon a threaded peripheral 3 portion of the strut casing tight against the lower edge of the ring hub.

Means for connecting the disks I1 to the ring hub I3 comprises an integral disk supporting ledge flange 21 projecting peripherally outwardly on the ring hub I9 spaced from its lower edge and upon which the inner margins of the disks I1, which for the present purpose are annularly dimensioned to be received coaxially about the ring hub I9, are stacked with appropriate spacer rings 28 therebetween as required. Fixed attachment of the stack of disk plates I1 upon the supporting ledge flange 21 is effected by means such as a plurality of screws 29 threaded into the flange 21 and having the heads thereof in compressing relation to an upper clamping ring 30. As a result, the spaced damper disks I1 are supported on the strut casing I3 and are held against rotary movement relative thereto. However, assembly of the disk unit with the casing I3 is a simple and easy production expedient.

Means for supporting the interleaved damper disks I3 operatively relative to the set of damper disks I1 include structure mounted for relative rotary movement on the strut casing I3 and providing a uid tight closure about the cooperating disk assemblies. To this end, a disk supporting rotary annular plate 3l is provided which is rotatably mounted on the hub member I3. A closure member 32 in the form of an annulus of generally L-shape cross-section is also rotatably mounted on the hub member I9 and cooperates with the plate 3| to provide the fluid tight closure about the cooperating sets of damper plates or disks I1 and I3.

For rotary cooperation with the hub member I 3, the plate 3l is formed with an inner marginal outwardly axially extending hub or bearing flange 33 in close sliding bearing engagement about the hub member I9 between the disk supporting flange 21 of the hub member and the hub engaging and clamping end of the hub retaining nut 24. The space between the end of the nut and the adjacent face of the disk retaining ange 21 is sufcient to afford slight clearance for free rotary movement of the flange 33 of the plate member 3 i.

Fluid seal between the flange 33 and the bearing surface of the hub member I3 is afforded by means such as an O-ring 34 maintained under compression within an annular groove 35 of generally V cross-section provided in the bearing surface of the flange 33.

The inner surface of the rotary supporting plate 3! provides a working surface 31 operatively opposing the adjacent face of the endmost damper disk I1. A groove 38 formed in the inner margin of the surface 31 provides clearance for the disk supporting flange 21 of the hub member.

The working surface disks I8 are secured in a spaced uniform stack, interleaved operativel7 with the disks I1, by means of screws 39 secured threadedly into threaded bores 40 in the outer margin of the working surface 31 of the plate SI. Spacer rings 4I may be interposed between the working disks I8, and a clamping ring 42 may be interposed between the heads of the screws 3S and the adjacent endmost working disk I8.

In certain respects the annular closure member 32 is constructed similarly to the plate 3 I, in that the closure member is formed with an inner marginal axially outwardly projecting hub flange 43 in slidable rotary bearing engagement with the hub member I9 and is formed with a generally V-shaped annular groove 44 within which an 0- ring sealing ring 45 is maintained under sealing compression.

In assembling the carrying plate 3I and the closure annulus 32, an internal stop shoulder 46 on an angular outer marginal flange 41 by engagement with the margin of the plate 3i defines the proper relationship of these components. A tight joint is provided by means of threads 48 on the internal margin of the flange 41 engaging with threads 49 on the plate periphery, a thread sealing ring 49a being set into the threaded plate periphery.

It will thus be apparent that the damper I5 provides a, compact unitary assembly that is efciently constructed of easily manufactured parts which can be assembled quickly and easily as a unit and then assembled with the strut casing I3. Thus, prior to assembly with the strut casing I3, the hub member I9 has the carrying disk or plate 3! assembled therewith and the interleaved sets of operating disks I1 and I8 are then stacked in interleaved relation with the apppropriate spacers 28 and 4I therebetween, and the disk assemblies then secured in place on respectively the supporting flange 21 of the hub and the carrying plate 3l. Thereafter the closure member 32 is assembled with the hub lli and threaded into assembly with the carrying plate 3l. By appropriate relative threading of the carrying plate 3l and the cover member 32, accurate, uniform spacing between the interleaved disks I1 and i8 can be accomplished since after the damper unit has been assembled with the strut casing I3 and secured in place by the retaining nut 24 engaging against the adjacent end of the hub member I9 to clamp the same agaist the shoulder iiange 20, the outer end of the cover member fiange 43 may engage in sliding bearing relation against the shoulder flange 20 and thus limit the axial movement of the cover 32 toward the shoulder flange 20 and thereby also limit the approach of the face of the groove 38 in the carrying plate 3| toward the adjacent face of the supporting ange 21 of the hub. In consequence, the position of the disks I3 with respect to the opposing disks I1 can be regulated with some accuracy. However, while primary adjustment can be effected as just described by reason of the threaded interengagement of the carrying plate 3i and the enclosing annulus 32, a certain amount of axial freedom of self -adj ustment is permitted in the Icarrying plate and closure annulus assembly s0 that the disks I8 can fmd an optimum uniformly spaced rela tion with respect to the operating disks I1 in the operation of the unit, the spacing between the ends of the anges 33 and 43 and the opposing retaining surfaces being afforded for this purpose but to a very limited extent since only slight adjustments in this respect will need to occur in operation.

fIo the extent thus far described, the cooperating damper disks I1 and I8 are freely relatively rotatably supported, that is, the disks I8 which are in fixed assembly with the supporting plate 3l and the closure or cover annulus 32 will move entirely free from the disks I1 upon rotation of the plate and cover assembly 3l, 32 about the strut casing I3. In this unit the damping of shimmy movement is the function of a viscous fluid. For example, a silicone fluid of 30,000 centistokes viscosity rating as measured in a Saybolt viscosimeter has been used with excellent results. This fluid is operable with substantial uniformity throughout an extreme range of temperature conditions and is therefore especially valuable for aircraftlanding gear. y-Alllfofthis ifuid is enclosed 4within the chamber provided -bythle ysup*poi'tingplate -3:I and -thecovermember landthe hub or bearingmember I9, 'and lls all of thespaces between lthe interleaved set of operating fdisks I1 and I8. The Aspacing between the opposing working surfaces of the 'disksand between gthe lworking surface 37|.A ofthe-supporting plate Aand fthe adjacent disk I .1 is greater than a lmere `ll-ib-ricatirig lmbut is n'nichv closer than will result -ina mere-flu'idlfrictionaldrag relationship between thedisks and the viscous fluid, being so v calculated that-a shear A-fllm ot-the viscous fluid exists between each pair of opposing working surfaces. The Vworking surface spacing isproperly correlatedto the viscosity Aof theluid to afforda.y linear velocity gradient, asi distinguished from a non-linear velocity gradient. That Tis, the laminar ulayers ofviiuid rbetween Lthe lopposing working surfaces are, ldue to r:the 1 relative closeness of the spacing between the surfaces ina conditioner 4shear rather than-lin a-.iiuid 'drag' relationship.

` In explanation it may .begstated that .thevelocity .of a laminarlayer-o-f fluid is Vequal to -thevelocity ofthe moving boundarytimes the distance from stationary boundary tothe layer inquestion divided by` the distance between boundaries if the Lproportion of the viscosity tothe distance between the boundaries is sufciently'high. This .can-be-shown graphically by a straight diagonal lilnetilting `in the direction vof'movement of the moving surface to represent linear velocity gradient, and a lcurving line from the stationary surfaceto ythe movingsurface to represent non* linear velocity gradient where the surfaces `are further apart than will result in alinear velocity gradient when considered` with respect to the viscosityv Aof th fluid in question. lThus, while the uid will allow comparatively free relative rotary movement of the working disks kII and -I 8, during slow relative rotary. movementsv of the assembly, rapid relative rotary :movements are resisted due to the shear resistance of the films of the viscous fluid between the working surfaces.

In order to afford a coupling vbetween the wheel yoke II and theslip ring shimmydamper I5, atorque scissors 5Il;is. provided'which come prises apair of links 5I and 52 pivotally connected together at -their vouteriends. The inner end of the link 5I is connected pivotally .between bosses-or ears .531 on theuwheelA yoke, and the correspondingend ofA the -link 52 -fis connected pivotally to .aibossM onthe shimmy damper casing.' VVA-Il-1rough thisarrangement vertical movements between the .wheel yoke II andthe shimmy damper IE7-as occasioned -by operation ofthe oleo str-ut II'Iiare accommodated but neverthelessthe slip ring structureof-the shimmy dampei' I5--is lconnected to move rotatablywith the wheel .yoke II. Asa result, rapid oscillatory, vibrational, shimmy movements ofthe wheel and the yoke II- aredampened by the viscous shear film-action-of the viscous fluid within the sh-immy damper I5 working inthe close linear gradient or-shear iilmspacings between'the working Vsurfaces withinthedamper. n

AA reductionin the Nnumber' of parts and simplification in assembly during -manufacture of the shimmy damperunitcanbe eiTected asshown in the'modiflc'ation of Figures and16 by elimihating thespacersibetweenone set of the interleavedeworkingedisks. To this end, :the damper unitgidentiiiedv asy `I5.; may beA .constructed substantially;V like 'the slip ring damperlunit: lA with the exception of itheomission-of the spacersfb'e-f tween one of the sets of disks, -hereinithefsetcf Working disks I8 which are supported by `the carrying plate 3l ofthe casing assembly. Since all parts of the damper unit with certain limited exceptions to -be noted are identical with the par-ts ofthe vunit I5, similar reference numerals have been applied-to the identical parts.

While the Working disks vI'I carried :by the hub ring I9 have the spacers 28 therebetween -toihold such disks in predetermined working-*clearance relation, the working disks I8 aremerely interleaved with respect to the workingdisks fITIfLan-d are :retained Yin substantially relative 'floating relation'but in .non-rotatable position with respect to `the supporting plate 3l byrmeans of -screw studs V55. Each of the studs 55 has a-sma'ller diameter threaded lower extremity v51 threaded into ,the carrying A,plate v3l and an opposite extremity head 53. The .disksY I8 are,:of.1.course, appropriately raperimred to pass the :studs-14 55 therethrough and are free floating longitudinally of the studs so that in operation the disksflanan assume a proper spaced relation automatically with respect to the cooperating working-@disks I1 under the` influence of the viscous f damping fluid working in the shear film spaces `between the opposed working disks. That is, when .the damper casing is rotated or. oscillated vrapidly relative Vtothe hub ring. I9 vthe'viscous resistance of the damping fluid within the dampingifuniit acting on the working surfacesof the-working disks causes the floating working l.disks Mito-ese sume automatically substantially optimum equal-A ized spacing with respect to opposing surfaces of the stationary working disks Il. As a y.resuliftl'ie unit operates with high damping efficiency..l

Where,` as shown, the uppermost disk of :the assembly is one of the working disks I8,"the.heads 58 of the retaining Studs 55 define the upward limit of movement of the upper'working` disks to retain the same during damping serviceinthe proper shear lm spaced relation4 to theuppermost working disk Il. In order to attain this relationship automatically during assembly, fthe lower extremity portions of the studs 55-above the reduced diameter threaded portions'lrare formed with respective shoulders .59 defining the relative vertical position of the studs by engagement with the adjacent upper surface :of V`the carrying plate 3 I, J

I claim as my invention:

1. In combination in an aircraft landing: wheel gear, a fixed strut, a wheel carrying member rotatably secured to the strut, a housing structure rotatably surrounding the strut, saidV housing structure having an annular chamber thereinpa set vof disks stationary with and encircling the ystrut extending into said chambenafsecondfset of disks interleaved with said stationary 'disks and rotatable with said housing structure,- andra connection externally of said strut between the housing structure and the wheel-carrying mem-y ber for'rotation of the housing. structurewitlr the wheel-carrying member, said chamber Ahaving. a

lviscous fluid therein and saiddisks having `opiposed working surfaces operatively in shear film spacing with respect to said Huid sok thatv rapid relative rotary movements of the. disks are re:- strained by the shearing action of theuidrbetween the working surfaces vof the disks;

2. In combination in an aircraft landing gear including a strut and a wheel-carrying member relatively rotatably connected thereto, an annular housing structure externally surroundingfand about thev strut and including a casing providing an annular chamber encircling the hub and relatively rotatable about said hub, a torque scissors connecting said casing with said wheel yoke, a set of spaced fiat disks carried by and held against rotati-cn by the hub and projecting into the chamber, and a set of fiat disks carried by and rotatable with the casing within the chamber and interleaved with the disks carried by the hub, the operative spacing between the opposing disk surfaces being closely spaced and coacting with a viscous damping fluid within the chamber to afford shear films of the fluid between the opposed surfaces of the disks.

4. In combination in an aircraft landing gear assembly, a strut having a cylindrical casing, a shimmy damper bearing hub secured xedly to and externally of said casing, a plurality of spaced working disks disposed radially and externally about and secured to said bearing hub, and a rotary assembly mounted on and surrounding said bearing hub and having a casing defining an annular chamber enclosing said disks, said casing carrying within said chamber and rotatable therewith a set of disks extending radially inwardly toward the hub member and interleaved With the hub disks with an operative shear lm spacing between the opposing working surfaces of the disks for coacting with viscous damping fluid therebetween to effect shimmy damping.

5. In combination in an aircraft landing gear assembly, a strut having a cylindrical casing, a shimmy damper bearing hub secured to said casing, a plurality of spaced working discs disposed radially about and secured to said bearing hub, and a rotary annular assembly about said bearing hub and having a casing defining an annular chamber enclosing said disks, said casing carrying within said chamber and rotatable therewith a set of disks extending radially toward the hub member and interleaved with the hub disks with an operative shear film spacing between the opposing working surfaces of the disks for accommodating viscous damping iluid therebetween, said casing including a generally l.shaped closure member and a plate member secured together to provide the chamber and with the slip ring disks secured to the plate member.

6. In combination in an aircraft landing gear strut including a cylindrical casing, said casing having a shoulder flange thereon, a bearing hub surrounding said casing and engaging at one end against said shoulder flange, a nut threaded onto said casing and engaging the opposite end of the hub to secure the hub against the shoulder flange, a key retaining said hub against relative rotation on the casing, and an annular structure defining Aan annular chamber therein rotatably secured in place on said hub between said shoulder and said nut, shimmy damping means within said chamber, and means for connecting the annular structure to a wheel carrying member.

7. In combination in an aircraft landing gear shimmy damper, a bearing hub ring, an annular assembly rotatable about the hub ring, said annular assembly having an annular chamber therein opening toward and closed by the hub ring, a set of spaced damper disks carried -by the hub ring and projecting radially therefrom into said chamber, and a cooperating set of spaced, interleaved damper disks carried by the annular assembly within the chamber and interleaved with the hub disks.

8. In combination in a slip ring shimrny damper for aircraft landing gear, a hub ring adapted to be secured to a landing gear strut, an annular structure slidably rotatable about said hub, said annular structure comprising a cover member and a plate threadedly interengaged and defining an annular chamber with said hub ring, said hub f ring having a radial supporting ange thereon extending into said chamber, a set of damper disks and spacers stacked Von said flange and secured fixedly thereto, and a set of damper disks and spacers stacked on and secured to said plate within said chamber, said sets vof disks being interleaved.

9. In combination in a slip ring shimmy damper for aircraft landing gear, a hub ring adapted to be secured to a landing gear strut, an annular structure slidably rotatable about said hub, said annular structure comprising a cover member and a plate threadedly interengaged and defining an annular chamber with said hub ring, said hub ring having a radial supporting flange thereon extending into said chamber, a set of damper disks stacked on said flange and secured thereto, a set of damper disks stacked on and secured to said plate within said chamber, said sets of disks being interleaved, said chamber being iilled with viscous damping fluid, and means between the cover member and the plate and the hub ring providing fiuid seals to prevent leakage of the iluid from the chamber.

10. In combination in 1a slip ring shimmy damper for aircraft landing gear, a hub ring adapted to be secured to a landing gear strut, an annular structure rotatable about said hub, said annular structure comprising a cover` member and a plate interengaged and dening an annular chamber with said hub ring, said hub ring having a radial supporting flange thereon extending into said chamber, a set of damper disks stacked on said ange and secured thereto, and a set of damper disks stacked on and secured to said plate within said chamber, said sets of disks being interleaved'.

11. In combination in a slip ring shimmy damper for use in aircraft landing gear, a ring hub, an annular radially extending plate rotatable about said hub, an annular generally L- shape cross-section cover member assembled with said rplate and also rotatable about the hub, the hub having a radially outwardly extending integral flange, a set of spaced disks mounted on said iiange and projecting radially relative to the hub into said chamber, a set of similar complementary cooperating disks mounted on said plate and operatively interleaved with the hub disks, the plate having a groove therein for clearing said hub flange, the inner surface of the plate being spaced in working relation to the adjacent hub carried disk.

12. In combination in an aircraft landing gear including a strut, a strut casing, said strut casing having an annular outwardly projecting shoulder flange, a slip ring hub about said casing and having an end engaging said shoulder flange, a nut securing said hub against said shoulder flange by engagement of the opposite end of the hub, said hub carrying a plurality of .agees-gans 7.19. Eradially extending spacedzshimmyfdamper; disks, :and ani annularstructure:rotatably carriedrby said hub between said shoulder and saidmut-and havinga chamber therein enclosing a set 'of shimmy damper disks carried by the annular structure andl interleavedfwith resp'ect'tothe hubcarried..I disks,..the.. sets of disks being so related that operative working, clearance therebetweenaffords shear films of viscous .fluid between the opposed working surfaces of the idisks, Aone of lsaid sets of disks being axially movable 'to-assum'eworking'spaced relation to the disks of"l the `other set -automatically'in'i service.'

13. A shimmy damper device for use in conjunction with a directionally adjustable aircraft landing wheel strut of the type including a pair of relatively rotatable support members, said shimmy damper device comprising an annular housing mounted to encircle one of said strut members in rotatable relation thereon, key means formed upon said one of said support members within the configuration of said housing member, means linking said housing member to the other of said support members for rotation therewith relative to the first mentioned support member, and resistance means comprising a plurality of resistance members slip-fitted into laminar relation within said housing, alternate of said resistance members being keyed to said support key means and to said housing respectively, and a viscous fluid substantially iilling said housing and the spaces between said resistance members whereby to cling to said resistance members and to resist relative movements of adjacent resistance members by resistance of the fluid to shear.

14. A shimmy damper device for use in conjunction with a directionally adjustable aircraft landing wheel strut of the type including a pair of relatively rotatable andl telescopically disposed inner and outer strut members, said shimmy damper device comprising a housing mounted outside of one of said strut members in rotatable relation thereon, means connecting said housing to the other of said strut members for rotation therewith'relative to said one of said strut members, and friction means comprising an element disposed within said housing and keyed to said one of said strut members, spacing means maintaining said element in slightly spaced relation to said housing, and a viscous fluid substantially filling said housing and the spaces between said element and said housing whereby to cling to said element and to thereby resist relative movements of said element and said housing by resistance of the fluid to shear.

15. In combination in an aircraft landing gear including a strut member and a wheel-carrying member relatively rotatably connected thereto, an annular housing structure externally surrounding and rotatable about one of said members, torque scissors means connecting the housing structure for joint rotation with the other of said members, and shimmy damping means within said housing structure.

16. In combination in a slip ring shimmy damper for aircraft landing gear, a hub ring adapted to be secured non-rotatably to a .landing gear strut, an annular structure rotatable about said hub ring defining therein an annular chamber of substantial radial depth and opening toward said hub ring, and a damper disk nonrotatably disposed with respect to said hub ring and extending into said chamber, said disk having opposite axially facing working surfaces and said annular.- structure having within, said cham!A :ber workingv surfaces disposed. in closely spaced parallelWorkingrelation-.to the working surfaces offsaid Vdisk so `that viscous-damping uid confined Within saidfchamber Will afford .shearresistance to relative rotary movement of said annularV structure andA said disk, said annular Vstructure having means thereon for operative vattachment-to a landing gear memberrotatable -relativefto' the gear strut. I

17:. In: combination in anY aircraft landing. gear including a.- strut member and a wheel-carry- .ingmember relatively rotatably connectedlthereto, an annular housing structure externally surrounding and rotatable about one of said mem bers, torque scissors means connecting the housing structure for joint rotation with the other of said members, and shimmy damping means within said housing structure and comprising a member non-rotatably attached to said one of said members and having Working surfaces disposed in closely spacedparallel relation to working surfaces provided within said housing and adapted to provide a shear lm coupling in the presence of a viscous uid within said housing.

18. A shimmy damper device for use in conjunction with a directionally adjustable aircraft landing wheel strut of the type including a pair of relatively rotatable and telescopically disposed members, said shimmy damper device comprising an annular housing mounted to encircle one of said strut members in rotatable relation thereon, key means formed upon said one of said strut members Within the configuration of said housing, means operably connecting said housing to the other of said strut members for rotation therewith relative to the first mentioned strut member, and friction means comprising a plurality of annular plates arranged in stacked relation within said housing, alternate of said plates being keyed to said strut key means and to said housing respectively, spacer means disposed between said stacked plates to maintain them in slightly spaced relation, and a viscous fluid substantially filling said housing and the spaces between said plates whereby to cling to said plates and to resist relative movements of adjacent plates by resistance of the fluid to shear.

19. A shimmy damper device for use in conjunction with a directionally adjustable aircraft landing wheel strut of the type including a pair of relatively rotatable members, said shimmy damper device comprising an annular housing mounted to encircle one of said strut members in rotatable relation thereon, key means formed upon said one of said strut members within the configuration of said housing, means connecting said housing to the other of said strut members for rotation therewith relative to the first mentioned strut member, and friction means comprising a selected plurality of plates arranged in stacked relation within said housing, alternately stacked plates being keyed to said strut key means and to said housing respectively, spacer means disposed between said stacked plates to maintain them in slightly spaced relation, and a viscous fluid substantially filling said housing and the spaces between said plates whereby to cling to said plates and to thereby resist relai i members, said shiinmy damper device comprising an annular housing mounted to encircle one of said strut members in rotatable relation thereon, means connecting said housing to the other of said strut members for rotation therewith relative to said one of said strut members, and friction means Comprising an annular plate disposed Within said housing and keyed to said one of said strut members, spacing means maintaining said plate in slightly spaced relation to said housing, and a viscous huid substantially filling said housing and the spaces between said plate and said housing whereby to cling to said plate and to thereby resist relative movements of said plate and said housing by resistance of the fluid to shear.

BERNARD E. OCONNOR.

References Cited in theV file of this patent UNITED STATES PATENTS Number` Name Date 10 1,718,175 Nilson June 18, 1929 2,061,656 Guthrie Nov. 24, 1936 2,333,550 Parker Nov. 2, 1943 2,367,993 Bishop Jan. 23, 1945 mms.' 

